Comparison of UV optical absorption and UV excited luminescence behaviours in Ge doped silica under H2 loading or CW UV laser irradiation

Abstract We compare the CW 244 nm laser induced absorption and photoluminescence excitation changes in Ge and Ge–P doped silica glass according to H2 loading. Under H2 loading only, the absorption does not change but the luminescence excitation intensity decreases by 60%. For samples not H2 loaded, luminescence excited in the UV range is annihilated by the laser irradiation but not the absorption in the same UV range. During UV irradiation of H2 loaded samples most of the luminescence excited in the UV range disappears whereas UV absorption behaves differently. In that way, we show that defects giving rise to luminescence exhibit a weak contribution to the absorption spectrum. In particular, there are two different oxygen deficient centres: one absorbing at 5 eV and another one giving rise to luminescence under 5 eV excitation. Due to some correlations existing sometimes between absorption and luminescence, we suggest that luminescence is quenched by trapping of electrons produced by 5 eV absorbing defects. In addition, the use of a CW laser allows us to observe two successive one-photon absorption steps for accounting for the absorption change: a singlet to singlet transition and then an ionisation.